1. Field of the Invention
The present invention relates to a liquid crystal display device capable of providing color display and having excellent display quality, and a method of manufacturing the same.
2. Description of the Prior Art
The active matrix liquid crystal display device can prevent the cross-talk by providing a switching element, that is turned off so as to cut off a signal when it is not selected, to respective pixels, and can exhibit excellent display characteristic rather than the simple matrix liquid crystal display device. In particular, the liquid crystal display device using TFT (Thin Film Transistor) as the switching element exhibits the excellent display characteristic equivalent to CRT (Cathode-Ray Tube) since the TFT has the high driving capability.
Normally, the liquid crystal display device has a structure in which the liquid crystal is sealed between two transparent substrates. Out of two surfaces (opposing surfaces) of these transparent substrates that oppose to each other, the common electrode, the color filter, the alignment film, etc. are formed on one surface side while the TFT, the pixel electrode, the alignment film, etc. are formed on the other surface side. In addition, polarizing plates are stuck onto an opposing surface and an opposite surface of the transparent substrate respectively. In the case of the TN (Twisted Nematic) liquid crystal display device, for example, two sheets of polarizing plates are arranged such that their polarization axes of the polarizing plates intersect orthogonally with each other. This liquid crystal display device is operated in such a mode that the light is passed through when the electric field is not applied and the light is shielded when the electric field is applied, i.e., the normally white mode. Also, in the case that the polarization axes of two sheets of the polarizing plates are aligned in parallel, this liquid crystal display device is operated in the normally black mode. In the following, the substrate on which the TFT, the pixel electrode, etc. are formed is called a TFT substrate and the substrate on which the common electrode, the color filter, etc. are formed is called a CF substrate.
In recent years, the liquid crystal display device is required to achieve the higher performance. Especially, the improvement in the visual characteristic and the display quality is strongly requested. The VA (Vertically Aligned) liquid crystal display device, especially MVA (Multi-domain Vertically Aligned) liquid crystal display device, is promising as the display device to satisfy such requirement.
FIG. 1 is a sectional view showing an example of the MVA liquid crystal display device in the prior art.
This liquid crystal display device consists of a TFT substrate 510, a CF substrate 520, and a vertically aligned liquid crystal 529 that is sealed between these substrates 510, 520. Also, the polarizing plates (not shown) are arranged under the TFT substrate 510 and on the CF substrate 520 respectively such that their polarization axes intersect orthogonally with each other, for example.
The TFT substrate 510 is formed as follows. That is, a plurality of pixel electrodes 516 that are aligned in a matrix fashion, the TFTs (not shown) connected to the pixel electrodes 516, data bus lines and gate bus lines (both not shown) for supplying the image data to the pixel electrodes 516 via the TFTs are formed on the transparent glass substrate 511. The pixel electrodes 516 are formed of transparent conductor such as ITO (Indium-Tin Oxide).
Also, domain defining projections 517 are formed on the pixel electrode 516. In addition, surfaces of the pixel electrodes 516 and the projections 517 are covered with an alignment film (not shown) formed of polyimide, or the like.
In contrast, the CF substrate 520 is formed as follows. That is, a black matrix 522 made of Cr (chromium), or the like is formed on the lower surface side of the glass substrate 521, and regions between the pixels are light-shielded by the black matrix 522. Also, any one of red (R), green (G), and blue (B) color filters 523 is formed every pixel on the lower surface side of the glass substrate 521. A common electrode 524 made of transparent conductor such as ITO, or the like is formed under the color filter 523. Domain defining projections 525 are formed under the common electrode 524. Also, surfaces of the common electrode 524 and the projections 525 are covered with the alignment film (not shown) formed of polyimide, or the like.
In the liquid crystal display device constructed as above, when the voltage is not applied, liquid crystal molecules 529a are aligned in the vertical direction to the alignment film. In this case, since the incident light passed through the polarizing plates from the lower side of the TFT substrate 510 is cut off by the polarizing plates arranged over the CF substrate 520, the display device exhibits the dark display. In contrast, when the sufficient voltage is applied between the pixel electrodes 516 and the common electrode 524, the liquid crystal molecules 529a are aligned in the perpendicular direction to the alignment film, as shown in FIG. 2. In this case, the liquid crystal molecules 529a are tilted in different directions on both sides of the projections 517, 525, so that alignment division (multi-domain) can be achieved. In this state, since the incident light passed through the polarizing plates from the lower side of the TFT substrate 510 is passed through between the polarizing plates arranged over the CF substrate 520, the display device exhibits the light display. The desired image can be displayed on the liquid crystal display device by controlling the applied voltage every pixel. Also, it is possible to suppress the leakage of the light along the oblique direction by the above alignment division and thus the visual characteristic can be improved.
In the above example, the case is explained where the projections are formed on both the TFT substrate 510 and the CF substrate 520. As shown in FIG. 3, the alignment division can be achieved similarly by providing slits 516a in the electrodes on one substrate side (in FIG. 3, the pixel electrode on the TFT substrate side).
Normally, in the liquid crystal display device in the prior art, spherical or cylindrical spacers whose diameter is uniform are employed to maintain a clearance between the pixel electrode and the common electrode (cell gap) constant. The spacers are formed of resin, ceramic, or the like, and are scattered on any one substrate when the TFT substrate 510 and the CF substrate 520 are stuck together. Hence, the cell gap between the pixel electrode and the common electrode is decided by the diameter of the spacer.
In Patent Application Publication (KOKAI) Hei 10-68955 and Patent Application Publication (KOKAI) Hei 11-264968, such an approach is set forth that cylindrical members formed by the photoresist is employed as the spacers in order to avoid generation of faults such as non-uniformity of the cell gap due to the spherical or rod-like spacers.